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101.
102.
Two nuclease activities which were shown previously to copurify from extracts of log-phase Neurospora mycleia, a single-strand specific endonuclease activity (with DNA and RNA), and a strand nonspecific exonuclease activity (with DNA only) have been found to be associated with a single polypeptide. The enzyme has therefore been classified as an endoexonuclease. In logphase extracts, about 75% of this enzyme was found to exist in an inactive form which was activated in vitro either by endogenous phenylmethylsulfonyl fluoride sensitive proteinase(s) or by exogenous trypsin. The inactive form of endoexonuclease has been purified 45-fold in 15% yield free of the active enzyme. On electrophoresis in 6 M urea--polyacrylamide gels, it migrated at a much slower rate than the active enzyme, indicating that it is a less acidic and(or) larger protein than the active nuclease. The strong adsorption of this inactive enzyme on octyl-Sepharose suggests that the protein may have a relatively large hydrophobic domain. The protein may be a precursor of the active enzyme (a pronuclease) or a strong complex of enzyme with a proteinaceous inhibitor that is not dissociated in 6 M urea or during a variety of chromatographic procedures. 相似文献
103.
J Steiner J Cassar K Mashiter I Dawes T R Fraser A Breckenridge 《BMJ (Clinical research ed.)》1976,1(6019):1186-1188
The effects of administration of methyldopa on serum prolactin and growth hormone (GH) concentrations in hypertensive patients were studied. Single doses of methyldopa (750 or 1000 mg) significantly increased serum prolactin levels, peak concentrations occurring four to six hours after drug administrations. Long-term methyldopa treatment was associated with threefold to fourfold increases in basal prolactin levels compared with those in normal subjects. In patients treated with methyldopa for two to three weeks the GH response to insulin hypoglycaemia was significantly greater than in normal subjects and untreated hypertensive patients. In contrast, patients treated for prolonged periods (mean 13-4 months) had a GH reponse indistinguishable from normal. 相似文献
104.
R S Fraser 《European journal of biochemistry》1975,60(2):477-486
Polyadenylated RNA was isolated from fission yeast (Schizosaccharomyces pombe) total RNA using oligo(dT)-cellulose, and was studied as a model for messenger RNA. The half-life of poly adenylated RNA was measured by two independent methods. (a) The rate of labelling of polyadenylated RNA during incubation of cells with [5-3H]uridine was measured. A half-life of 40-45 min was found by comparing the experimental data with theoretical curves calculated for labelling of RNAs with various half-lives. The influence of precursor-pool specific activity on RNA labelling kinetics is considered. (b) Cells were labelled with [5-3H]uridine then further RNA synthesis was inhibited by addition of 8-hydroxyquinoline. The rate of loos of radioactivity from polyadenylated RNA indicated a half-life of 50 min. The half-life found by these two methods is about one-third of the cell doubling time, and is much longer than previous estimates by indirect methods of yeast messenger RNA half-life. Both experimental methods provided evidence for the existence of tas a half-life of 40-50 min; a much smaller population is probably turning over more rapidly. After inhibition of RNA synthesis by 8-hydroxyquinoline, the rate of total protein synthesis declined much more rapidly than the polyadenylated RNA content of the cells. However, 60 min after inhibition of RNA synthesis there was a small rise in the rate of portein synthesis. These data are interpreted as evidence for mechanisms controlling protein synthesis which operate at the level of messenger RNA translation. 相似文献
105.
The plating of mycoplasma virus MVL-1 is greatly improved by the use of tetrazolium to enhance the visibility of the lawn. 相似文献
106.
Human platelet secretion and aggregation induced by calcium ionophores. Inhibition by PGE1 and dibutyryl cyclic AMP
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Ca2+, Mg2+-ionophores X537A and A23,187 (10(-7)-10(-6) M) induced the release of adenine nucleotides adenosine diphosphate (ADP, adenosine triphosphate (ATP), serotonin, beta-glucuronidase, Ca2+, and Mg2+ from washed human platelets. Enzymes present in the cytoplasm or mitochondria, and Zn2+ were not released. The rate of ATP and Ca2+ release measured by firefly lantern extract and murexide dye, respectively, was equivalent to that produced by the physiological stimulant thrombin. Ionophore-induced release of ADP, and serotonin was substantially (approximately 60%) but not completely inhibited by EGTA, EDTA, and high extracellular Mg2+, without significant reduction of Ca2+ release. The ionophore-induced release reaction is therefore partly dependent upon uptake of extracellular Ca2+ (demonstrated using 45Ca), but also occurs to a significant extent due to release into the cytoplasm of intracellular Ca2+. The ionophore-induced release reaction and aggregation of platelets could be blocked by prostaglandin E1 (PGE1) or dibutyryl cyclic AMP. The effects of PGE1, and N6, O2-dibutyryl adenosine 3':5'-cyclic monophosphoric acid (dibutyryl cAMP) were synergistically potentiated by the phosphodiesterase inhibitor theophylline. It is proposed that Ca2+ is the physiological trigger for platelet secretion and aggregation and that its intracellular effects are strongly modulated by adenosine 3':5'-cyclic monophosphoric acid (cyclic AMP). 相似文献
107.
Genetics of Cortisone-Induced Cleft Palate in the Mouse—embryonic and Maternal Effects 总被引:2,自引:2,他引:0
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Differences between mouse strains in frequency of embryonic, cortisone-induced cleft palate were examined. Probit analysis demonstrated a family of linear and parallel dose-response curves for different inbred and hybrid embryos. Since the differences between genotypes were not in the slopes of the response curves but rather in their location, it is proposed that the median effective dose (ED50) of cortisone required to induce cleft palate (or the tolerance) provides a more appropriate definition of the response trait and its difference than a frequency statement. The tolerance of C57BL/6J is dominant to that of A/J. A maternal effect of A/J relative to C57BL/6J dams caused a two-fold reduction in the embryonic tolerance of cortisone. Cortisone-induced cleft palate and mortality were separate response traits.—In these and previous studies on cortisone- and other glucocorticoid-induced cleft palate in the mouse, the nature of the cleft-palate-response curve appeared to be the same for all glucocorticoids, and within-strain differences in tolerance could be used as measures of potency or bioassays for a particular effect of the glucocorticoids. 相似文献
108.
109.
110.
Extreme temperatures,foundation species,and abrupt ecosystem change: an example from an iconic seagrass ecosystem
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Jordan A. Thomson Derek A. Burkholder Michael R. Heithaus James W. Fourqurean Matthew W. Fraser John Statton Gary A. Kendrick 《Global Change Biology》2015,21(4):1463-1474
Extreme climatic events can trigger abrupt and often lasting change in ecosystems via the reduction or elimination of foundation (i.e., habitat‐forming) species. However, while the frequency/intensity of extreme events is predicted to increase under climate change, the impact of these events on many foundation species and the ecosystems they support remains poorly understood. Here, we use the iconic seagrass meadows of Shark Bay, Western Australia – a relatively pristine subtropical embayment whose dominant, canopy‐forming seagrass, Amphibolis antarctica, is a temperate species growing near its low‐latitude range limit – as a model system to investigate the impacts of extreme temperatures on ecosystems supported by thermally sensitive foundation species in a changing climate. Following an unprecedented marine heat wave in late summer 2010/11, A. antarctica experienced catastrophic (>90%) dieback in several regions of Shark Bay. Animal‐borne video footage taken from the perspective of resident, seagrass‐associated megafauna (sea turtles) revealed severe habitat degradation after the event compared with a decade earlier. This reduction in habitat quality corresponded with a decline in the health status of largely herbivorous green turtles (Chelonia mydas) in the 2 years following the heat wave, providing evidence of long‐term, community‐level impacts of the event. Based on these findings, and similar examples from diverse ecosystems, we argue that a generalized framework for assessing the vulnerability of ecosystems to abrupt change associated with the loss of foundation species is needed to accurately predict ecosystem trajectories in a changing climate. This includes seagrass meadows, which have received relatively little attention in this context. Novel research and monitoring methods, such as the analysis of habitat and environmental data from animal‐borne video and data‐logging systems, can make an important contribution to this framework. 相似文献